Today's Image of Mars shows some interesting features in and near the the central uplift of Ritchey Crater. At the top of this image you can see an ancient streambed. Just above the center of the image are multi-colored rocks and minerals in the crater's central uplift.
Central uplifts are created when a newly formed crater's walls succumb to gravity and collapse in toward the center. This process often results in material being dredged up from deep within the crater walls.
Ritchey Crater is approximately 79km in diameter. Scientists are extremely interested in Ritchey Crater because it contains so many well preserved layers. The dark, more wear-resistant layer at the top of the central uplift acts as a cap to the underlying layers, protecting them from erosion. The layers underneath are softer and lighter. It is speculated that the layers may be composed of volcanic ash, sedimentary deposits, or sand dunes.
This image is the same size as the original, uncaptioned HiRISE image, so instead it will link to the Wikipedia page for Ritchey Crater, which unfortunately doesn't have much more information than I've provided above.
If you like the HiRISE images showcased in the Mars Photo of the Day posts I encourage you to enter for a free 2012 HiRISE Calendar